using System;

using System.Collections.Generic;

using Newtonsoft.Json;

public class Program

{

    public class Variables {

        public string VariableName1 { get; set; }

        public string VariableName2 { get; set; }

        public string VariableName3 { get; set; }

    }

​

    public class Model {

        public Model() {

            VariableList1 = new List<Variables>();

            VariableList2 = new List<Variables>();

        }

        public List<Variables> VariableList1 { get; set; }

        public List<Variables> VariableList2 { get; set; }

    }

    public static void Main()

    {

        var model = new Model();

        model.VariableList1.Add(new Variables { VariableName1 = "temp1", VariableName2 = "temp2", VariableName3 = "temp3" });

        model.VariableList1.Add(new Variables { VariableName1 = "temp4", VariableName2 = "temp5", VariableName3 = "temp6" });

        model.VariableList2.Add(new Variables { VariableName1 = "temp1", VariableName2 = "temp2", VariableName3 = "temp3" });

        var json = JsonConvert.SerializeObject(model, Formatting.Indented);

        Console.WriteLine(json);

    }

}